New developments in green LEDs



Green InGaN LEDs showed great improvements over the last decade, but still perform not as good as blue InGaN LEDs. Brightness, Efficiency and sub-linearity of brightness versus driving current (“droop”) are significantly lower for a 530 nm green LED than for a 440 nm blue LED. Assuming an indirect Auger effect as one of the major loss mechanisms in InGaN LEDs, a reduction of the carrier density per emitting well is the key for efficiency improvement for green LEDs. An optimized multiple quantum well (MQW) structure with multiple emitting wells at 525 nm is compared to a single quantum well LED structure. A color-coding scheme was used to investigate MQW operation: up to four MQWs contribute to the green emission at 525 nm. Packaged 1 × 1 mm2 ThinGaN® chips emit up to 109 lm (209 mW) at 350 mA and 170 lm (339 mW) at 700 mA, the efficacy was 90 lm/W and 66 lm/W, respectively. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)